Human monoclonal antibodies contain two identical heavy chain polypeptides (each about 54 kilodaltons in MW) and two identical light chain polypeptides (each about 24 kilodaltons in molecular weight) which are bound together by disulfide bonds. Each light chain and each heavy chain include a constant region and a variable region. The variable region is located on the N-terminal portion of each chain and the constant region is located on the C-terminal portion of each chain. The constant regions of the light chains and heavy chains have different amino acid sequences, and can be used to identify the isotype of the heavy or light chain. In humans, there are two different isotypes of light chain polypeptides referred to as either kappa or lambda; and five different isotypes of heavy chain polypeptides referred to as gamma (IgG), alpha (IgA), mu (IgM), epsilon (IgE), and delta (IgD).
Clinical laboratories currently monitor and quantify the levels of monoclonal antibody therapeutics in patients receiving such treatment using immunoassays, such as ELISA.